In a cab mounted on a bulldozer for instance, a cab body is integrally mounted on a floor frame. The cab body includes right and left front pillars that stand upright on the front end of the floor frame; right and left center pillars that stand upright on the longitudinally intermediate part of the floor frame; and right and left rear pillars that stand upright on the read end of the floor frame. These pillars are connected to one another at the upper ends thereof with desired beam members that are disposed on the top of the cab body so as to extend in longitudinal, lateral and diagonal directions. Herein, the pillars (support column members) and the beam members are each composed of a pipe member having a square cross-section.
As illustrated in FIG. 14(a), in a cab body 101, a gusset 105 (i.e., a plate for strengthening an angle in framework) is joined at the corner where a left rear pillar 102 and a beam member 104 meet at substantially right angles and a gusset 106 is joined at the corner where a right rear pillar 103 and the beam member 104 meet at substantially right angles. The beam member 104 connects the upper ends of the rear pillars 102, 103 to each other and is hereinafter referred to as “rear lateral beam member 104”. Likewise, gussets 108, 109 are joined at the respective corners where the left rear pillar 102 and the right rear pillar 103 respectively meet a floor frame 107 at substantially right angles. The gussets 105, 106, 108, 109 are each composed of a relatively-thick, plate-like material.
If a lateral load F is imposed on the top of the cab body 101 from the left side, the left rear pillar 102 will tilt to the right while the right rear pillar 103 will be pushed by the rear lateral beam member 104, tilting to the right, so that deformation will occur so as to reduce the angle between the rear lateral beam member 104 and the right rear pillar 103. At that time, the gusset 106 functions as a reinforcement member for restraining the deformation. Such reinforcement by use of gussets is commonly practiced and one example of it is disclosed in JP-A-2004-338686.
When the lateral load F is imposed on the top part of the cab body 101, it causes a load acting on the rear lateral beam member 104 from the gusset 106 side so as to crush the rear lateral beam member 104. This load concentrates upon a position of the rear lateral beam member 104 that corresponds to a rear lateral beam member side end 106a of the gusset 106. In the conventional cab reinforcement structure having the gusset 106, the concentrated load is received by the rear lateral beam member 104 composed of a pipe member and therefore the gusset 106 thrusts into the rear lateral beam member 104 as illustrated in FIG. 14(b), which presents the problem that the satisfactory reinforcing effect of the gusset 106 cannot be obtained. Thrust-in similar to the above-described thrust-in of the gusset 106 resulting from the action of the lateral load F possibly occurs between the right rear pillar 103 and the gusset 106 and between the left rear pillar 102 and the gusset 108. In cases where the upper peripheral edge of the floor frame 107 is composed of a pipe member, similar thrust-in may occur between this pipe member and the gusset 108.
The above problem may be solved by reinforcing the hollow support column members or hollow beam member to which a gusset is joined. A prior technique of such reinforcement is proposed, for instance, in JP-A-11-166247 (Patent Document 2). According to Patent Document 2, a hollow pillar 110 composed of an inner plate 111 and an outer plate 112 which are joined to each other is provided with a vertical reinforcement member 113 as shown in FIG. 14(c). The vertical reinforcement member 113 is inserted in the hollow pillar 110 so as to partition its inner space and has the shape of “]” (square bracket) in cross-section.
The vertical reinforcement member 113 used for strengthening the hollow pillar 110 in the technique of Patent Document 2, however, fails to function as a reinforcement member capable of sustaining a load that is imposed on the hollow pillar 110 so as to locally crush it, although it effectively functions as a reinforcement member capable of effectively resisting a bending load imposed on the hollow pillar 110. Therefore, the above problem will not be solved even if the technique disclosed in Patent Document 2 is applied to the above-described cab reinforcement structure having gussets.
The invention is directed to overcoming the above problem and a first object of the invention is therefore to provide a cab reinforcement structure and a work machine cab which are capable of preventing a gusset provided between a support column member and a hollow beam member from thrusting into the beam member. A second object of the invention is to provide a cab reinforcement structure and a work machine cab which are capable of preventing a gusset provided between a hollow support column member and a beam member from thrusting into the support column member. A third object of the invention is to provide a cab reinforcement structure and a work machine cab which are capable of preventing a gusset provided between a floor frame and a hollow support column member from thrusting into the support column member. A fourth object of the invention is to provide a cab reinforcement structure and a work machine cab which are capable of preventing a gusset provided between a pipe member constituting a floor frame and a support column member from thrusting into the pipe member.